Tuesday, June 13, 2017

Accumulated wetting thresholds reached at lower elevations

The past week there have been a minimal amounts of rainfall in the Winchester and central Virginia areas, but there continues to be wetting hour accumulation at the lower elevations. 

For purposes of predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. This year our petal fall date at Winchester was Apr 24, so the start of wetting hour accumulation was from May 4. As of Monday morning June 12, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 271 hr (21 CWH over the 250-hr threshold); at 932 ft (the AREC NEWA station), 184 hr; and at the 983 ft elevation, 153 hr ACW. In the past week most of the wetting hour accumulation was from dew and occurred more at lower elevations in the orchard. Note that at the lowest elevation, the ACW of 271 hr reached the threshold level of 250 ACW on June 7. This predicts that the fungi causing SBFS symptoms are now present on unprotected fruit and that symptoms on such fruit should appear in about 2-3 weeks.

For Nelson County in central Virginia, the petal fall date was Apr 20, and accumulation of wetting hours from Apr 30 is recorded by three weather stations at different elevations at Tyro. Wetting hour accumulation in central Virginia was slow last week. As of June 5, a sensor placed at 1465 ft. elevation had accumulated only 76 wetting hours from Apr 30, while the one at 1165 ft. had accumulated 164 wetting hours, and the one placed at 941 ft elevation had accumulated 254 hr- just over the 250-hr threshold).

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) is approaching the threshold level of 250 ACW this week, having recorded 246 wetting hours since May 1. A NEWA station at Fishersville is also approaching the 250-hr threshold with 238 ACW.